Am I doomed to start university at 21 years old in September 2017 and not be able to get on with my life?
I joined university late as well. The thing is, no one cares about your age, and at 21 you will not be a social outcast. If you graduate at 25, no employer will give you crap about your age either, it's not like you got your diploma after 40 when the employers lose interest in you exponentially.
In fact quite a few people I know graduated at 25, simply because they were moving around, getting married and working while attending universities.